Information is recorded on and read from a moving magnetic tape with a magnetic read/write head positioned next to the tape. The magnetic “head” may be a single head or, as is common, a series of read/write head elements stacked individually and/or in pairs within the head unit. Data is recorded in tracks on the tape by moving the tape lengthwise past the head. The head elements are selectively activated by electric currents representing the information to be recorded on the tape. The information is read from the tape by moving the tape longitudinally past the head elements so that magnetic flux patterns on the tape create electric signals in the head elements. These signals represent the information stored on the tape.
Data is recorded on and read from each of the parallel tracks on the tape by positioning the head elements at different locations across the tape. That is, head elements are moved from track to track as necessary to either record or read the desired information. Movement of the magnetic head is controlled by an actuator operatively coupled to some type of servo control circuitry. Tape drive head positioning actuators often include a lead screw driven by a stepper motor, a voice coil motor, or a combination of both. The carriage that supports the head is driven by the actuator along a path perpendicular to the direction the tape travels. The head elements are positioned as close to the center of a track as possible based upon the servo information recorded on the tape.
FIG. 1 illustrates generally the configuration of a tape drive 10 typical of those used with single spool tape cartridges. Referring to FIG. 1, a magnetic tape 12 is wound on a single supply spool 14 in tape cartridge 16. Tape cartridge 16 is inserted into tape drive 10 for read and write operations. Tape 12 passes around a first tape guide 18, over a magnetic read/write head 20, around a second tape guide 22 to a take up spool 24. Head 20 is mounted to a carriage and actuator assembly 26 that positions head 20 over the desired track or tracks on tape 12. Head 20 engages tape 12 as tape 12 moves across the face of head 20 to record data on tape 12 and to read data from tape 12. Referring to FIGS. 2 and 3, roller guide 28 includes disc shaped flanges 30 and an annular hub 32. Flanges 30 and hub 32 may be machined as a single integral part or as three separate parts bonded together. In either case, flanges 30 function to keep tape 12 at the proper angle as it passes across head 20. If the tape is presented to the head at too great an angle, then the read and write elements in the head may be misaligned to the data tracks. Flanges 30 are also needed to help keep tape 12 properly packed on take up spool 24.
As the tape is pulled over the guides, a film of air is created between the outside surface 34 of hub 32 and tape 12. This film is often referred to as an air bearing. The air bearing allows the tape to move with low friction very rapidly back and forth between flanges 30. Consequently, high frequency tape movement can occur when the edge of the tape bumps abruptly against flanges 30. Read/write head positioning systems have difficulty following such high frequency tape movement. It would be desirable to reduce this air bearing and thereby increase the friction between the tape and the hub to slow the movement of the tape back and forth between the flanges. Slowing the tape in this manner would allow the head positioning system to better follow the tape as it wanders back and forth between the guide flanges.
One technique that has been used to reduce the air bearing is creating an irregular topography on the surface of the hub. This technique is described in U.S. patent application Ser. No. 09/597,882. In one version of this technique, described in the '882 application, a series of comparatively deep grooves are formed in the surface of the hub to reduce the air bearing. In another version, comparatively high raised areas are formed on the surface of the hub. It has been discovered that these surface topographies can leave imprints on the tape which may, under some conditions, distort or otherwise damage the tape.